Technical Field
The present invention relates to an apparatus and a method for adjusting an envelope signal delay in an envelope-tracking power amplifier, and more particularly, to a technology of the time synchronization between an input signal inputted to an envelope-tracking power amplifier and an envelope signal applied to a power supply unit of the envelope-tracking power amplifier.
Background
Recently, differently from a past Global System for Mobile Communications (GSM), a mobile communication system has been evolved to an Orthogonal Frequency Division Multiplexing (OFDM) based communication system that has amplitude which changes greatly. The OFDM based communication system, such as Worldwide Interoperability for Microwave Access (WiMAX) and Wireless Broadband Internet (WiBro), is widely used, including the recently spotlighted Long-Term Evolution (LTE).
However, an OFDM-based transmitter has a problem in that a power amplifier does not operate efficiently due to the characteristic of a high Peak to Average Power Ratio (PAPR). In order to overcome this problem, various transmission structures have been proposed, including an envelope-tracking power amplifier.
The envelope-tracking power amplifier may accomplish a high efficiency performance when a signal having a waveform similar to an envelope of an input signal of the power amplifier is applied to a power supply unit of the power amplifier to always operate the power amplifier in a saturation area.
However, when time synchronization between an envelope signal applied to the power supply unit of the envelope-tracking power amplifier and an envelope signal of an input signal inputted to the envelope-tracking power amplifier does not match properly, the non-linearity of an output of the power amplifier may be generated significantly to lower the quality of a signal and an adjacent channel leakage ratio (ACLR) may be deteriorated to make it difficult to transmit a wireless signal.
FIG. 1 illustrates a simulation result of adjacent channel leakage ratio (ACLR) in accordance with a mismatched degree of time synchronization between an envelope signal applied to the power supply unit of the envelope-tracking power amplifier and an input signal inputted to the envelope-tracking power amplifier with respect to a signal of LTE 10 MHz having the characteristic of PAPR 8.7 dB. Referring to FIG. 1, it can be seen that the ACLR may be worse than −45 dB even if the time synchronization is deviated about 1 ns.